/Engine/Plugins/FX/Niagara/Source/NiagaraShader/Public/NiagaraShared.h
Allow Niagara script the opportunity to modify the compilation environment for GPU simulations. Generally used for data interfaces to inject project defines.
virtual void ModifyCompilationEnvironment ( EShaderPlatform Platform, struct [FShaderCompilerEnvironment](API\Runtime\RenderCore\FShaderCompilerEnvironment) & OutEnvironment ) const